I need to design a wall with a cut height of about 20 feet parallel to active rail.  The soil report has glacial till for the top 15 feet followed by weathered bedrock to a depth of about 40 feet where the boring ends.
The weathered bedrock description is:  medium to soft, moderate to moderately severely weathered, dark gray, amorphous, ARGILLITE, with very close (<2"), moderately dipping (35deg-55deg) joints/fractures. RQD from 0 to 10%.
I believe my only option is for a soldier pile and lagging or a secant pile wall but I need recommendations with regard to this weathered bedrock. Any ideas?
 

I would agree that a drilled-in soldier pile system would be the best alternative.  Be sure to follow the the governing guidlines (AREMA?) and if possible contact the owner of the rail line for their thoughts and input.  The railway can be very picky in what they want, especially if the system is to be a permanent wall.

First, don't double post.

Second, you need to contact the geotechnical engineer of record and/or an engineer who knows about design and construction of walls such as this.  It appears that you are out of your element with this work.